Technical Abstract:
The present study investigated changes in insulin-like growth factor-1 (IGF-1) of hens subjected to two distinct molting regimens and fed pre- and post-molt diets either high or low in omega-3 fatty acids (FA). From 62 to 76 wk of age, 45 White Leghorns (9 hens/treatment) were monitored for plasma IGF-1 concentrations at -7, 2 (or 54 h), 13, 21, 36, 43 and 64 d post-molt using an homologous RIA. The molting treatments consisted of 10 d fasting + cracked corn for 7 d + pullet developer diet for 10 d or a non-fasting molt (wheat-middlings based diet for 28 d). Five wk prior to and after either molt treatment, birds were fed one of two diets containing dietary omega-6 /omega-3 FA ratios of 0.6 or 7.9. A non-molted control group of birds was fed a laying hen diet containing a dietary omega-6/omega-3 ratio of 8.0. A second experiment employed the same 5 treatment groups (5 birds/treatment) with blood sampling at -7, 25 and 64 d post-molt. Using treatment as the whole plot with repeated measurements, an analysis of covariance (62 wk IGF-1 as covariate) and an ANOVA were conducted for experiments 1 and 2, respectively. Induced molt affected plasma IGF-1 in experiment 1 (treatment by age interaction, P < 0.0001), and the response was the same regardless of molting regimens. Induced molt initially caused a decrease in IGF-1 54 h post-molt; however, from 13 to 43 d post-molt, molted birds showed elevated levels of IGF-I as compared to controls. By 64 d post-molt, IGF-1 in molted hens was similar to controls. In experiment 2, significantly elevated IGF-1 levels were noted 25 d post-molt with a return to normal levels by 64 d post-molt in molted hens as compared to controls. Feeding diets high in omega-3 FA as compared to diets low in omega-3 FA 5 wk prior to or after molt did not consistently affect IGF-1 in molted hens. In conclusion, circulating IGF-1 in White Leghorns was affected by molting regimen but not by the pre- or post-molt diets varying in omega-3 FA.